evince/eog crash when using untrusted X11

evince/eog crash when using untrusted X11 connection (ssh -X with ForwardX11Trusted no) .

Somehow geis->backend ends up being NULL in this case, and it crashes in geis_backend_create_token which is called with a NULL argument from geis_backend_token_new (geis.c). I am not sure how this should be handled, but adding a test at the top of geis_backend_token_new fixes the problem:

  if (!geis->backend)
   return NULL;

This causes then a crash later in libgrip in the function 'processed_mapped_window_request' (gripgesturemanager.c), because it calls geis_filter_add_term with a NULL filter. This may be fixed with a test after 'geis_filter_new':

 GeisFilter window_filter = geis_filter_new(priv->geis, filter_id);

  if (NULL == window_filter)
        return;

Not sure if there are better ways, but this seems to fix it for me.